Device for supplying gas to an analyzer of traces of impurities in a gas

ABSTRACT

A device for supplying gas to an analyzer for measuring traces of impurities in the gas comprising: (i) a source of pure gas; (ii) a set of at least first and second bypass gas lines, arranged in parallel and fed by the source of pure gas, the first and second bypass gas lines having a common gas entry and a common gas exit, the common gas exit being in communication with a feed line of the analyzer through a common gas exit line; (iii) a device for charging a gas in the first bypass gas line with a predetermined quantity of at least one impurity for forming a standardizing gas; (iv) a restriction disposed in each of the first and second bypass gas lines, each restriction being calibrated to divide the flow of pure gas feeding the set between the first and second bypass lines in a predetermined ratio; and (v) a flow regulator for regulating the flow of pure gas feeding the set of bypass gas lines, disposed between the source of pure gas and the common gas entry of the first and second bypass gas lines, wherein the first and second bypass gas lines, between the common gas entry and the calibrated restriction are devoid of any pressure-measuring member.

This application is a divisional, of application Ser. No. 08/370,294 ,filed Jan. 9, 1995.

BACKGROUND OF THE INVENTION

(i) Field of the Invention

The present invention relates to a process and to a device for supplyinggas to an analyzer of traces of impurities in a gas and, moreparticularly, to such a process and to such a device, according to whichthe analyzer is supplied sequentially with a gas to be analyzed, a puregas and a standardizing gas obtained by dilution of one or moreimpurities in this pure gas.

(ii) Description of the Related Art

Such a process and such a device, designed for feeding an analyzer ofvery high sensitivity are known from document FR-A-2 667 397 in theApplicant's name. Such an analyzer can be designed to detect impuritiesin very low concentrations (for example 10⁻² -10⁻⁵ ppm). It must then befrequently standardized by supplying a pure or "zero" gas and a"standardizing" gas containing impurities in accurately determinedconcentrations.

In the device of the abovementioned document a constant gas flow isensured in each of the lines supplying to the analyzer the gas to beanalyzed, a pure gas and a standardizing gas charged with apredetermined quantity of impurities, respectively, by arranging in eachline a calibrated orifice operating in the sonic regime and a pressuresensor upstream of this orifice, the sensed pressure control-driving aflow regulator placed in a discharge bypass of the line, downstream ofthe orifice. To prevent the pressure sensor from contaminating the gastraveling in the line, the sensor is fitted in a bypass equipped with aleakage line permitting a small leakage flow in this bypass. All theseprecautions increase the bulk of the device as well as its complexityand its cost of manufacture. The bulkiness of the device is furtherburdened by the use of a bottle filled with standardizing gas.Furthermore, the accuracy of flow regulation is affected by that of thepressure measurement performed by the sensor, which itself must becorrected for temperature when the latter varies.

SUMMARY AND OBJECTS OF THE INVENTION

The aim of the present invention is therefore to provide a process and adevice of the type described above, which are designed so as to permit amore compact embodiment of the device, while ensuring a more accurateadjustability of the gas flows to be supplied to the analyzer.

Another aim of the present invention is to provide such a process andsuch a device which are guaranteed against any contamination of thegases provided by members such as pressure sensors and pressure or flowregulators, and enabling the gas for standardizing the analyzer to bechanged rapidly and conveniently.

These aims of the invention, as well as others which will appear onreading the description which is to follow, are achieved with a processfor supplying gas to an analyzer of traces of impurities in a gas,according to which the analyzer is supplied sequentially with a) a gasto be analyzed, b) a pure gas and c) a standardizing gas obtained bydilution of one or more impurities in this pure gas, this process beingnoteworthy in that a set of at least two bypass lines fitted in parallelis fed with this pure gas, the bypass pure gas of one of the lines ischarged with a predetermined quantity of at least one impurity toobtain, after dilution with the bypass pure gas of the other bypassline, the standardizing gas which is directed toward the analyzer alonga feed line and the flow of pure gas allowed to enter the set is dividedwith the aid of two calibrated restrictions, each placed at the entry ofthe bypass lines. The flow rate of pure gas feeding the set is regulatedwith the aid of a flow regulator placed upstream of the set.

As will be seen later, the use of calibrated restrictions in linesconnected in parallel, in combination with a regulation of the flowfeeding the bypass, makes it possible to constitute compact and accuratemeans of flow division, without pressure or temperature measurement, andwithout it being necessary to use the stages and means of calculation,traditionally associated with these measurements.

The calibrated restriction may consist of any means making it possibleto carry out this division, regardless of whether it is, for example, anorifice, a capillary or a sinter.

In order to make use of the process according to the invention a deviceis employed including a) a source of pure gas, b) a set of at least twobypass gas lines fitted in parallel and fed by the source of pure gas,c) means for charging the bypass pure gas traveling in one of the twolines with a predetermined quantity of at least one impurity, d) arestriction placed at the entry of each of the bypass lines andcalibrated to divide between these two lines, in a predetermined ratio,the flow of pure gas feeding the set and e) a flow regulator of pure gasfeeding the set, situated between the source of pure gas and the gasentry of the set, and in the case of each bypass line the portion of theline between the gas entry of the set and the calibrated restriction isdevoid of any pressure-measuring member.

In accordance with a characteristic of the device according to theinvention, the latter additionally includes two flow regulators, eachplaced in a discharge line connected, in the case of one, to the exit ofthe bypass line for gas charged with impurities and, in the case of theother, to the exit of the set.

This arrangement makes it possible to ensure an accurate adjustment ofthe gas flows in the two lines and of the dilution ratio of thestandardizing gas charged with impurities which is delivered by one ofthese lines into the pure gas delivered by the other line. The deviceadvantageously includes means allowing at least a second stage ofdilution of the standardizing gas to be established.

According to one of the embodiments of the invention the deviceadditionally includes a gas purifier placed between the source of puregas and the gas entry of the set.

In accordance with another advantageous characteristic of the deviceaccording to the invention the means for charging with impurities thestream of bypass pure gas traveling in one of the bypass lines inparallel to form the standardizing gas consist of a plurality ofpermeation cartridges dispensing impurities into said line selectivelyor collectively, in parallel, with predetermined permeation rates. Thesepermeation cartridges, which are particularly compact, enable the deviceto be reduced in bulk. The use of a complete set of such cartridgesenables a standardizing gas of any predetermined composition to beproduced conveniently and rapidly.

As will be clearly apparent to a person skilled in the art the processaccording to the invention makes it possible to perform thestandardization of the analyzer by supplying it, according to thecircumstances (analyzer type, user's choice), sequentially, pure gas andstandardizing gas contaminated with impurity(ies) or else, for example,sequentially, two different standardizing mixtures containing differentcontents of impurity(ies).

Other characteristics and advantages of the present invention willbecome apparent on reading the description which is to follow andexamining the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows diagrammatically the circuitry and various members of afirst embodiment of the device according to the invention,

FIG. 2 shows diagrammatically an alternative form of a part of thedevice of FIG. 1, and

FIG. 3 is a graph representing the change in the impurity concentrationof a standardizing gas when the latter is formed with the aid of thedevice according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is made to FIG. 1, in which a first embodiment of the devicein accordance with the invention has been shown, designed for supplyinggas to an analyzer 1 of very high sensitivity, capable of measuringtraces of impurities present in concentrations in the range of, forexample, 10⁻² -10⁻⁵ ppm. This device must thus be capable of ensuring 1)the generation of a reference pure gas or "zero gas", that is to say infact of a purified gas containing less than 10⁻⁵ ppm of impurities, 2)the generation of a standardizing gas containing traces of gases orimpurities, for example H₂ O, CO₂, CO, O₂, CH₄, H₂, and the like, invariable concentrations in a range extending from 10⁻⁵ ppm to 10⁻² ppm,and 3) the control of parameters for introducing gas into the analyzer,such as pressure and flow rate.

To do this, the device shown in FIG. 1 includes a feed line 2 of theanalyzer 1, which can be selectively connected to a source 3 of a gas tobe analyzed by means of a coupling line 4, or to a line 5 dispensingeither a standardizing gas or a pure gas, as required for standardizingthe analyzer, as is well known. This line 5 is itself fed by first,second and third lines 7, 8, 9 respectively, which are fed by a secondsource of gas 10, which may, furthermore, consist of the source 3itself. The source 10 is connected to the three lines 7, 8, 9 via apressure regulator 11, the exit of the pressure regulator beingconnected, on the one hand, to the set of the bypass lines 7, 8 whichare fitted in parallel, via a flow regulator 12 and a purifier 13 and,on the other hand, to the additional line 9 via a flow regulator 14 anda purifier 15. Means 16, which will be described in greater detail inwhat follows, are provided for charging the gas stream flowing throughthe line 7 with impurities consisting of traces of gases such as, forexample, CO, CH₄, O₂, CO₂ or H₂ O.

Flow regulators 17, 18, 19, 20 are fitted in discharge lines 21, 22, 23,24 respectively, of the line 7, of the exit of the lines 7 and 8, of theline 5 and of the line 4, respectively.

The control of the parameters for introducing gas into the analyzer 1 isensured with the aid of an upstream pressure regulator 25 fitted as abypass in a discharge line 26 of the line 2, this discharge lineadditionally including a purge valve 27, and with the aid of a flowregulator 28 fitted at the gas exit 29 from the analyzer.

Finally, the flow rate of gas in the line 4 can be adjusted andmeasured, conventionally, with the aid of a calibrated orifice 30upstream of which is placed a noncontaminating pressure sensor such asan in-line piezoelectric sensor 6, for example of the "through tube"type.

It is essential that the gas flow rates D₁, D₂ in the lines 8 and 7respectively should be set accurately, since the dilution ratio of theimpurities injected by the means 16 at the exit of these lines dependson these flow rates. In accordance with an essential characteristic ofthe present invention this result is obtained with the aid of calibratedrestrictions; in the case of the embodiment shown, of simple calibratedorifices 31, 32 fitted at the entry of the bypass lines 7, 8respectively and of the flow regulator 12 (if appropriate with the aidof additional regulators 17 and 18), associated therewith.

Operation in a sonic regime will be given preference for the calibratedorifices of the system, but the process and device according to theinvention have shown satisfactory and comparable results even whendeparting somewhat from the particular regime consisting of the sonicregime.

In sonic flow of gas through the orifices 31 and 32, that is to say whenwith each orifice the ratio of the upstream pressure to the downstreampressure is higher than 2, it is known that the mass flow rates D₁ andD₂ of the gas in these orifices 32, 31 respectively are equal to:

    D.sub.1 =K.sub.GAS ×P×T.sup.-2/3 ×S.sub.1 =α×P×S.sub.1

    D.sub.2 =K.sub.GAS ×P×T.sup.-2/3 ×S.sub.2 =α×P×S.sub.2

with D=D₁ +D₂, being the total flow rate of the gas supplied to lines 7and 8,

P=pressure upstream of the orifices

T=temperature,

which is common to both orifices if they are close to each other,K_(GAS) =constant which depends only on the nature of the gas and on thegeometry of the orifice, these geometries being assumed to be identical(for example circular) for both orifices 31 and 32, S₁, S₂ =sections ofthe orifices 31, 32 respectively.

The above relationships give:

    D.sub.1 =D×S.sub.1 /(S.sub.1 +S.sub.2)

    D.sub.2 =D×S.sub.2 /(S.sub.1 +S.sub.2)

It will be noted that, for a given total flow rate D, the accuracyΔD_(i) /D_(i) for each of the flow rates depends on the accuracy reachedin the ratio of the sections S₁ and S₂, that is, in the case of D₁ :

    ΔD.sub.1 /D.sub.1 =Δ(S.sub.2 /S.sub.1)/(1+S.sub.2 /S.sub.1)

The pressure P upstream of the orifices is automatically balanced to thevalue:

    P=D/(α×(S.sub.1 +S.sub.2))

In order that the orifices 31 and 32 may be employed in a sonic regimein the range of the flow rates D in question, the sum of the sections S₁+S₂ of these orifices must be such as to give, for each orifice:

    P/P.sub.DOWNSTREAM >2

where P_(DOWNSTREAM) is the pressure downstream of the orifice inquestion.

Thus, advantageously, the flow division thus obtained does not requireany pressure measurement or temperature measurement, favouring thecompactness, the simplicity and the cost of manufacture of the device inaccordance with the invention. The division principle thus establishedcan be generalized to a set of N calibrated orifices, as will be seenlater in connection with FIG. 2.

In the case of conditions departing slightly from the sonic regime(pressure ratio equal to 2 or slightly less than 2), the flow deliveredto the set is nevertheless distributed in the ratio of the areas of thecalibrated orifices (or else in the ratio of the pressure dropsintroduced by a capillary or a sinter).

Nevertheless, the more the conditions depart from such a ratio 2, themore sensitive will the system be to variations in downstream pressure.

With regard to the regulation and the control of the flows in thevarious lines of the device in accordance with the invention, it will benoted that all the components capable of contaminating the gas, forexample at a level of 10⁻⁵ ppm or more, such as a valve or a flowregulator, have been systematically placed either upstream of thepurifiers (flow regulators 12, 14, pressure regulators 11) or bypassingor downstream of the critical lines (flow regulators 17, 18, 19, 20,25).

Returning to the means 16 employed for charging the gas traveling in theline 7 with traces of gases or impurities, and for diluting the gas thuscharged so as to obtain "standard" gases of accurately determinedcomposition, according to the invention, these means advantageouslyconsist of a battery of permeation cartridges (16₁, 16₂, 16₃, and so on)charged with gases such as O₂, CO₂, H₂ O, CH₄, CO, H₂ and the like.These cartridges may be fitted in parallel in the line 7, to dispensecontinuously and simultaneously into the latter, or else to beseparately connected to the line 7 via simple two- or three-way valves,which may be considered to be noncontaminating at the high impurityconcentrations of the gas in the line 7, before dilution in the gasdelivered by the lines 8 and 9. These cartridges are commonly small inbulk (for example 2×2×10 cm) and can therefore remain fitted permanentlyin the device, occupying little space. When cartridges whose permeationrate τ is small are chosen the lifetime of such a cartridge can then belonger than 1 year.

The concentration C of impurities introduced by a cartridge 16_(i) witha permeation rate τ in the gas of flow rate D₂ flowing in the line 7 is:

    C=Kτ/D.sub.2

τ depending on the nature of a permeation membrane with which thecartridge is equipped, of the gas and of the temperature, K being theconstant for the gas in question.

It will be understood that the introduction of a battery 16 ofpermeation cartridges 16_(i) into the device in accordance with theinvention provides the latter with greater compactness and a longlifetime, and offers a wide choice of the gases which can be introducedto form the gases for standardizing the analyzer. These standardizinggases are obtained after dilution of the gas leaving the line 7 in thepure gas of flow rate D₁ leaving the line 8, and then the dilution ofthe resulting gas in the pure gas of flow rate D' leaving the line 9,these dilutions being controlled by the flow regulators 17, 18.

In accordance with an advantageous characteristic of the deviceaccording to the invention, all the lines of the device are continuallypurged with gas, so as to maintain the internal surfaces of the lines indynamic absorption/desorption equilibrium, to avoid transient regimes inrespect of pressure/flow rate, during which any surface in contact withthe gas is capable of desorbing and of adsorbing molecules, a processthat is liable to modify the composition of the gases which are formed.

In accordance with yet another advantageous characteristic of the deviceaccording to the invention, all the exits of the mass flow regulatorsand those of the purge line 27 are combined and assembled into a singleexit (not shown) directed, for example, toward a purifier, beforedischarge or optional recycling. Any modification of the composition ofthe gases which are formed, due to possible back-diffusion of gasthrough these exits is thus prevented. In addition, it is then possibleto employ flammable or toxic gases which require special precautions.

The operation of the device according to the invention will now beexplained, firstly in a stage of analysis of a gas of flow rate D_(a)originating from the source 3, secondly in a stage of standardization ofthe analyzer with the aid of a "zero" gas and of standardizing gas.

In an analysis stage it is obviously necessary that the lines 21, 22 and5 should absorb completely the gases dispensed by the lines 7, 8 and 9in order that these gases should not enter the analyzer feed line 2. Theflow rates D_(ij) which are set by the regulators ij in question mustthen satisfy the relationship:

    D.sub.19 +D.sub.17 +D.sub.18 >D.sub.12 +D.sub.14

That is (D₁₉ +D₁₇ +D₁₈)-(D₁₂ +D₁₄)=R>0.

The excess flow rate R must then originate from the line 4.

If the leakage flow rate in the line 24 is also set at R (in order tomaintain a gas flow therein), the flow rate of gas D₂₈ in the analyzersatisfies the relationship:

    D.sub.28 <D.sub.a -2R

The discrepancy from equality being due to the leakage flow rate in thepressure regulator 25 and to possible losses in the analyzer.

In a particular embodiment of the device in accordance with theinvention, in which the flow rates D₁, D₂ in the lines 8 and 7respectively are equal and established with the aid of circular sonicorifices 31, 32 calibrated at 62 μm, where the maximum flow rates of theregulators 12, 14, 17, 18, 19, 20 and 24 are 190 cc/min, 5 l/min, 100cc/min, 7 l/min, 10 l/min and 5 l/min respectively, R=200 cc/min waschosen.

In order to send a pure or "zero" standardizing gas into the analyzer 1it is necessary to short-circuit the flow D_(a) from the line 4 into theleakage line 24 and that from the line 7 into the line 21. With theflow-rate regulation parameters shown above it is then possible tochoose:

    D.sub.14 =5 l/min

    D.sub.12 =190 cc/min=D

    D.sub.17 =D.sub.18 =100 cc/min

    D.sub.19 =R

    D.sub.20 =D.sub.A +R

    R=200 cc/min

for example

In order to send into the analyzer 1 only the standardizing gas formedin the line 7 it is necessary to short-circuit the flow D_(a) as shownabove and to regulate the dilution of the impurities in the gas suppliedby the source 10 by an appropriate adjustment of the flow rates in thelines 21 and 22, by virtue of the flow regulator 17 and 18 respectively,that is, for example:

    D.sub.14 =5 l/min

    D.sub.12 =190 cc/min=D

    D.sub.19 =R

    D.sub.17 <D.sub.2

    D.sub.18 <D-D.sub.17

    D.sub.20 =D.sub.A +R

The concentration C of the standardizing gas or mixture supplied to theanalyzer is of the form:

    C=C.sub.0 ×Q.sub.1 ×Q.sub.2

where C₀ =Kτ/D₂ as already seen, and Q₁, Q₂ are the dilution factors ofthe first and second dilution stages respectively, which can be adjustedwith the aid of the flow regulators 17 and 18 respectively, it beingpossible for the product Q₁ ×Q₂ then to take any value, for examplebetween 5×10⁻⁵ and 2×10⁻².

With a pure gas consisting of oxygen and a permeation cartridge ofpermeation rate τ=50 ng/min it has thus been possible to form standardmixtures with contents of between 1.8×10⁻⁵ ppm and 7.5×10⁻³ ppm.

Thus it appears that the dilution of the impurities in the standardizinggas and the switching of the three types of gas to be supplied to theanalyzer can be obtained merely by control-driving the various flowregulators of the device according to the invention. The lattertherefore lends itself to an automation in which the adjustment of theseregulators could be ensured by use of a means 38 for control-driving aset of flow regulators, for example, by a computer duly programmed forthis purpose.

FIG. 2 shows an alternative form (7, 8, 9') of the arrangement of thelines 7, 8, 9 of FIG. 1 and of the associated regulators and purifiers.In this arrangement a single flow regulator 33 and a single purifier 34are employed for feeding the three lines, the additional line 9' beingconnected between the common entry of the lines 7 and 8 and the commonexit of these lines. The flow rates D₃, D₄, D₅ in the lines 7, 8, 9' arethen set by calibrated sonic orifices 35, 36, 37 respectively, ofsections S₃, S₄, S₅ respectively, of diameter d₃, d₄, d₅, in accordancewith the relationships:

    D.sub.3 =D×S.sub.3 /(S.sub.3 +S.sub.4 +S.sub.5)

    D.sub.4 =D×S.sub.4 /(S.sub.3 +S.sub.4 +S.sub.5)

    D.sub.5 =D×S.sub.5 /(S.sub.3 +S.sub.4 +S.sub.5)

With d₃ =d₄ =60 μm and d₅ =400 μm, for example, the performance of thedevice of FIG. 1 is found again with:

    D.sub.3 =D.sub.4 =95 cc/min

    D.sub.5 =5000 cc/min

to the benefit of lesser bulkiness, complexity and cost of manufactureof the device, as a result of the elimination of one regulator and onepurifier.

The device in accordance with the invention can be used in combination,for example, with an analysis apparatus consisting of an ionization massspectrometer at atmospheric pressure, in order to supply it, inter alia,with a zero gas containing less than 2×10⁻⁶ ppm of oxygen and less than10⁻⁵ ppm of water. FIG. 3 gives the graph provided by such aspectrometer when its feed is switched between a zero gas and a mixturecontaining 0.009 ppm of oxygen, the graph showing that this switchingtakes place substantially instantaneously.

It now appears that the invention makes it possible to achieve the setobjectives, namely to produce a device for supplying gas to an analyzer,which is at the same time accurate, simple in design and small in bulk,especially as a result of the elimination of any pressure samplingupstream of the restrictions, and other stages of calculation which wereassociated therewith, quick to use and purge, exhibiting a very shortresponse time when the concentration of impurities is changed during thestandardization, enabling the standardizing gas to be changed simply andrapidly by virtue of the battery of permeation cartridges which isemployed, and which is easy to automate.

The invention is obviously not restricted to the embodiments describedand shown, which have been given merely by way of example. Thus, itwould not constitute a departure from the present invention to increasethe number of lines fitted between the source 10 and the line 5, inorder to increase the number of dilution stages of the standardizing gasbeyond the two stages which are seen in FIGS. 1 and 2.

We claim:
 1. A device for supplying a gas to an analyzer for measuringtraces of impurities in the gas comprising:(i) a source of pure gas;(ii) a set of at least first and second bypass gas lines, arranged inparallel and fed by the source of pure gas, said first and second bypassgas lines having a common gas entry and a common gas exit, said commongas exit being in communication with a feed line of the analyzer througha common gas exit line; (iii) means for charging a gas in said firstbypass gas line with a predetermined quantity of at least one impurityfor forming a standardizing gas; (iv) a restriction disposed in each ofsaid first and second bypass gas lines, each restriction beingcalibrated to divide the flow of pure gas feeding the set between thefirst and second bypass lines in a predetermined ratio; and (v) a flowregulator for regulating the flow of pure gas feeding said set of bypassgas lines, disposed between the source of pure gas and the common gasentry of said first and second bypass gas lines, wherein said first andsecond bypass gas lines, between the common gas entry and eachcalibrated restriction are devoid of any pressure-measuring member. 2.The device as claimed in claim 1, further comprising:(i) a flowregulator connected to a discharge line which is connected to said firstbypass line for gas charged with impurities, upstream of the common gasexit of said first and second bypass gas lines; and (ii) a flowregulator connected to a discharge line which is connected to the commongas exit line of said first and second bypass gas lines.
 3. The deviceas claimed in claim 2, further comprising a purifier situated betweenthe source of pure gas and the common gas entry of said first and secondbypass gas lines.
 4. The device as claimed in claim 3, wherein the puregas flows through one or more lines between the purifier and an entry ofthe analyzer, the one or more lines being devoid of any member capableof contaminating the gas flowing therein.
 5. The device as claimed inclaim 1, further comprising an additional line fed by the source of puregas, the additional line being connected to the feed line of theanalyzer, and having a flow regulator and a purifier connected thereto.6. The device as claimed in claim 5, wherein the pure gas flows throughone or more lines between the purifier and an entry of the analyzer, theone or more lines being devoid of any member capable of contaminatingthe gas flowing therein, wherein said purifier has an exit through whichthe pure gas flows via a line, devoid of any member capable ofcontaminating the gas flowing in the line, to an entry of the analyzer.7. The device as claimed in claim 1, further comprising:(i) a third gasline comprising a gas entry and a gas exit, wherein: (A) the first andsecond bypass gas lines and the third gas line are fed by the samesource of pure gas via the same flow regulator; (B) the entry of thethird gas line has a calibrated restriction ensuring, with respect tosaid first and second bypass gas lines, division of the pure gassupplied by the source to the first and second bypass gas lines and thethird gas line; and (C) the gas exit of the third gas line is connectedto the feed line of the analyzer; and (ii) a purifier disposed betweenthe source of pure gas and the common gas entry of said set of bypassgas lines and said third gas line.
 8. The device as claimed in claim 7,wherein the pure gas travels through one or more lines between thepurifier and an entry of the analyzer, the one or more lines beingdevoid of any member capable of contaminating the gas flowing therein,wherein said purifier has an exit through which the pure gas flows via aline, devoid of any member capable of contaminating the gas flowing inthe line, to an entry of the analyzer.
 9. The device as claimed in claim1, wherein said means for charging a gas in said first bypass gas linewith a predetermined quantity of at least one impurity is a plurality ofpermeation cartridges dispensing impurities into said first bypass gasline selectively or collectively, in parallel.
 10. The device as claimedin claim 1, further comprising an analyzer connecting line forconnecting the analyzer to a source of gas to be analyzed, wherein aflow regulator is connected to a discharge line of the analyzerconnecting line.
 11. The device as claimed in claim 10, furthercomprising means for control-driving a set of flow regulators in orderto regulate a dilution ratio of the impurities in the standardizing gasand in order to selectively and sequentially switch between streams ofgases fed to the analyzer, the gases including a gas to be analyzed, thestandardizing gas and the pure gas, said set of flow regulatorsincluding:(i) a flow regulator connected to a discharge line which isconnected to said first bypass gas line for gas charged with impurities,upstream of the common gas exit of said first and second bypass gaslines; (ii) a flow regulator connected to a discharge line which isconnected to the common gas exit line of said first and second bypassgas lines; and (iii) the flow regulator connected to the discharge lineof the analyzer connecting line.
 12. The device as claimed in claim 1,further comprising a flow regulator connected to an exit line of theanalyzer and a flow regulator connected to a discharge line of theanalyzer feed line.
 13. The device as claimed in claim 1, furthercomprising means for ensuring a continuous flow of gas to the analyzer.14. The device as claimed in claim 1, wherein the calibratedrestrictions are calibrated orifices.